This commit fixes the env. variable in the
KMS guide used to specify the CA certificates
for the KES server.
Before the env. variable `MINIO_KMS_KES_CAPATH` has
been used - which works in non-containerized environments
due to how MinIO merges the config file and environment
variables. In containerized environments (e.g. docker)
this does not work and trying to specify `MINIO_KMS_KES_CAPATH`
instead of `MINIO_KMS_KES_CA_PATH` eventually leads to MinIO not
trusting the certificate presented by the kes server.
See: cfd12914e1/cmd/crypto/config.go (L186)
ed4bd20a7c